Fiber optics may be used as a waveguide for a coherent light wave propagating over a long distance. The refractive indices of the fiber optics may be different along the cable, and cause the light wave to travel at non-uniform speeds. Inherent built-in defects, physical perturbation, and temperature fluctuations may cause the refractive indices of a fiber optic to change. As a coherent light wave propagates through the fiber optics, the localized change of refractive indices may alter the speed of the light wave, which results in phase changes, and may cause the direction of propagation to reverse through scattering. Additionally, the birefringence of the fiber optic may cause the state of polarization of the light wave to change. In a fiber optic system, the input of the fiber optics may be aligned, both in space and the angle of approach, with output of the light source to facilitate the efficient injection of the light wave. More than one fiber optics may be fused together at their ends to increase the overall length of the waveguide. Fiber optics can provide propagation mediums for single mode or multi-mode lasers, and are inherently immune to electromagnetic interference. For single mode transmission, the fiber optic line may have a smaller diameter than the fiber optic line for multi-mode transmission.
A fiber optic cable includes at least one fiber optic, typically made from the transparent glass fiber, in its core, and surrounded by transparent cladding with a lower index of refraction. The cable further includes a protect sleeve covering the cladding to minimize physical damages to the fiber optic line. A single cable can include one or more fiber optics. Fiber optics have the advantage of being a low-loss waveguide, and can relay optical signals over a long range without the need to amplify the signals. Some fiber optics may be doped with different materials for specialized purposes.